Have some tech billionaires discovered the fountain of youth? Elon Musk is the visionary behind Space-X and Tesla Motors. 20 years ago he had a receding hairline, but today, at age 46, he has bulging muscles and a full head of hair. Amazon founder Jeff Bezos made headlines when he was photographed looking buff in a tight shirt. His stunning physique at age 54 inspired funny memes. So what's their secret to reversing the clock?